1. Field of the Invention
The invention relates to an apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction, which corrugated cardboard comprises at least an upper liner with a surface and a total width a and at least two profiled patterns of the upper liner, namely lateral edges and at least one of a longitudinal cut dividing the web of corrugated cardboard into partial webs and at least an upper groove, which profiled patterns run in the conveying direction and which profiled patterns have distances b, c, d from each other, and which corrugated cardboard has plane portions of the surface between the profiled patterns.
2. Background Art
In such an apparatus known from U.S. Pat. No. 6,836,331, two sensors are arranged on both sides of the web of corrugated cardboard, of which a first sensor is designed such as to measure the distance of the first liner from the first sensor and of which a second sensor is designed such as to measure the distance of a second liner from the second sensor. In order to detect the position of at least two profiled patterns, the two sensors are arranged relative to each other and are synchronously displaceable crosswise of the conveying direction of the web of corrugated cardboard. Downstream of the sensors is disposed an evaluation device for detecting the distance of the at least two profiled patterns from each other. The accuracy of measurement of this device is satisfactory. A disadvantage is that the constructional effort for crosswise displacement of the sensors is quite extensive and that the time required for the respective measuring process in relation to the high speed of webs of corrugated cardboard in corrugated-cardboard machines is very high.
Thus it is the object of the invention to provide an apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction, said apparatus combining a high measuring speed and a high accuracy of measurement with a simple design.
According to the invention, this object is achieved in an apparatus of the generic type,
wherein a light source emits a light band to the surface of the upper liner across the total width a thereof in a direction crosswise of the conveying direction at an angle α to the surface of the upper liner,
wherein a measuring camera is arranged above the web of corrugated cardboard which absorbs light reflected by the surface and which detects the profiled patterns by means of a light intensity of the light reflected by the profiled patterns, the light intensity of which deviating from a light intensity of light reflected by plane portions of the surface, and
wherein an evaluation device is connected to the measuring camera for determination of the distance b, c, d of the at least two profiled patterns from each other on the basis of the differing light intensities of the light reflected towards the measuring camera.
The gist of the invention is that the light band which is emitted to the surface of the upper liner at an angle thereto and crosswise of the conveying direction is reflected differently by the profiled patterns, in other words by the grooves and/or longitudinal cuts than by the smooth, i.e. plane portions between the profiled patterns. This allows an electronic image of the entire surface of the web of corrugated cardboard, including the profiled patterns, to be generated in a conventional measuring camera, the electronic image being evaluated in a correspondingly programmed computer serving as evaluation device, which allows to determine the respective, exact actual value of the distances of the individual profiled patterns from each other.
By the measures wherein on both sides of the web of corrugated cardboard is arranged in each case one reference point with a constant distance f from each other whose distance g from each other is continuously detected by the measuring camera, it is attained that temperature-related measuring errors in the camera can be compensated. Thus, the camera constantly receives an exact reference value for the distance between the two reference points which allows for numerical compensation of measuring errors.
The distance of the camera from the surface of the web of corrugated cardboard should be as large as possible. The distance is limited by constructional conditions in factory buildings and the like. The distance should however be chosen at least such that for the distance e of the measuring camera from a measuring line, formed by the incidence of the light band on the surface of the web of corrugated cardboard, relative to the total width a of the web of corrugated cardboard, applies e≧a.
Further features, advantages and details of the invention will become apparent from the ensuing description of an embodiment, taken in conjunction with the drawing.